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GIST 26 3 rd May 2007

Initial results from RADAGAST Nazim Bharmal Tony Slingo, Gary Robinson, Jeff Settle, Helen White ESSC, University of Reading. GIST 26 3 rd May 2007. R adiative A tmospheric D ivergence using A RM Mobile Facility, G ERB data and A MMA st ations.

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GIST 26 3 rd May 2007

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  1. Initial results from RADAGASTNazim BharmalTony Slingo, Gary Robinson, Jeff Settle, Helen WhiteESSC, University of Reading GIST 26 3rd May 2007

  2. Radiative Atmospheric Divergence using ARM Mobile Facility, GERB data and AMMA stations. • Using the AMF and GERB to study the divergence of radiation across the atmosphere. • Long-term & comprehensive surface measurements of atmospheric radiation and structure in Africa. • Resolve disagreements between radiation codes and data. • Study the radiative properties of aerosols (desert dust, biomass), water vapour and clouds.

  3. AMF, Niger during 2006 • AMF is ARM mobile facility. • Niger was first overseas deployment. • Two sites established; • Main site at Niamey (airport). • Subsidiary site at Banizoumbou (rural). • Active (Niamey only) and passive measurements of atmospheric composition & radiation.

  4. Geographical precis

  5. Geographical precis

  6. GERB data and spatial resolutions 0.6m radiances, 2006/11 10.8 m radiances, 2006/11 • SEVIRI (365 days) • GERB ARG (338 days) • GERB HR (265 days)

  7. Surface overview AOT PWV

  8. Surface flux overview LW SW

  9. TOA flux overview LW SW

  10. Modelling undertaken • Modelling of radiation using ARM data. • Using Edwards-Slingo and Fu-Liou (flux only). • Comparisons at ground and TOA, broadband and spectrally resolved. • At AMF, Niamey and GERB. • Currently, LW is clear-sky & SW is clear-sky plus aerosol.

  11. Modelling OLR; GERB & ES OLR difference persist between ES model and GERB ARG.

  12. Model comparisons ; ES & ECMWF OLR comparison; ECMWF has better correspondence to GERB.

  13. Model comparisons ; ES & ECMWF DLR comparison; atmospheric composition is comparable.

  14. Model comparisons ; ES & ECMWF GLR comparison; ECMWF has lower skin temperature.

  15. AMF site comparisons OLR scatter GLR scatter Banizoumbou c.f. Niamey has lower skin temperature but equivalent OLR.

  16. How to represent GERB “column”? • Potential issues: • Inappropriate skin temperature. • AMF, Niamey not representative. • Inaccurate emissivity. • Sand/soil is measured ~0.95. • ECMWF uses 0.99. • ES uses 1. • Lack of aerosol in atmosphere. • Significant clear periods in November. • Inconsistent atmospheric profile. • Surface comparisons show to be adequate.

  17. Changing emissivity and skin temperature • Emissivity, 0.99, lowered to 0.95 • Tskin lowered by 1.6 K

  18. Conclusion and future intentions • Understand GERB fluxes for Niamey during 2006. • LW HR and ARG agree well over Niamey. • Modelling shows both radiances and fluxes behave similarly c.f. GERB. • SW HR and ARG disagreement due to heterogeneity. • Heterogeneity issues affect modelling of OLR. • Emissivity is ~0.95. • AMF, Niamey skin temperature is too high. • Accurate clear-sky fluxes permit cloud and aerosol forcing. • Complementary method to interpolation.

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